1. Field of the Invention
The present invention relates to an apparatus and method for waste water treatment which can accomplish high level waste water treatment using charcoal biologically activated (i.e. charcoal in which microorganisms have been grown), for waste water and malodorous gas containing hard-to-decompose chemical substances such as surfactants, and which can treat malodorous gas at the same time.
2. Description of the Prior Art
Conventionally, in apparatuses for waste water treatment in various industrial facilities and laboratories, activated charcoal has been utilized at their terminals, i.e., at the stage of high level treatment.
Also, malodorous gas accompanying the waste water has been treated by a malodorous gas treating apparatus of the scrubber system, the activated charcoal adsorption system, or the like entirely independently of the above apparatus for waste water treatment.
As the way of utilizing activated charcoal in the high level treatment of waste water at the terminal of waste water treatment, available are physical methods in which only the adsorptive action of activated charcoal, i.e., physical treatment is expected, and physical-biological methods in which with microorganisms propagated in activated charcoal, two fields of treatment, i.e., physical adsorptive treatment inherent in the activated charcoal and biological treatment by the above microorganisms are utilized. More specifically, the latter physical-biological methods are such that activated charcoal adsorbs chemical substances and the adsorbed chemical substances are decomposed by the microorganisms that have propagated in the activated charcoal.
High concentration toxic waste water containing hard-to-decompose surfactants, which is discharged from various types of industrial facilities, semiconductor factories, liquid crystal factories, and the like, is recently increasingly subject to waste water treatment within their own sites. In such a background surrounding those factories, first described in detail is a concrete example of granular activated charcoal utilized, for example, in the high level waste water treatment systems.
High concentration toxic waste water, for example, developer-containing waste water discharged from the existing semiconductor and liquid crystal factories contains 2000 to 10000 ppm tetramethylammonium hydroxide (hereinafter, abbreviated as TMAH) that shows biological toxicity. The developer-containing waste water also contains various types of hard-to-decompose surfactants, alcohols, and colored resists, in addition to the TMAH.
Specifically, the hard-to-decompose surfactants contained in developers are, for example, alkylammonium based or polyoxyethylene based surfactants.
As the method of waste water treatment for use in the factories, available are chemical treatment methods such as neutralization, reaction, and flocculation, biological treatment methods such as biological films, contact oxidation, activated sludge, and special microorganism treatment, and physical treatment methods such as precipitation, filtering, adsorption, floatation, and film treatment (hereinafter, these biological and physical treatment methods will be abbreviated generically as pretreatment process), which would be selected depending on water quality of the waste water. Actually, the aforementioned treatment methods are used singly or in combination of some of them, so that high concentration toxic waste water is treated and discharged (see Japanese Patent Laid-Open Publications HEI 1-9500 and SHO 64-43306). Further, in actual cases, the conventional apparatus for waste water treatment would be provided with an activated charcoal adsorption tower at the treatment terminal, as necessary, under stringent discharge regulations.
As described above, in the case of treatment within factory sites, it has been common practice that waste water is subjected to chemical treatment, biological treatment, and physical treatment for a long time followed by treatment at the activated charcoal adsorption tower, generally within factory sites. Then, high concentration toxic waste water containing surfactants is treated up to a water quality level lower than the legal regulation level and, as such, discharged.
Also, since the activated charcoal to be contained in the activated charcoal adsorption tower is expensive in its unit price itself, short in service life before regeneration, and high in its running cost, the use of so-called activated charcoal with microorganisms is nowadays increasingly spreading in which microorganisms are propagated in activated charcoal and organic substances adsorbed by the activated charcoal are treated by the microorganisms.
The tower, whether it is a tower containing the aforementioned activated charcoal or another containing the aforementioned activated charcoal with microorganisms, has conventionally had a structure that activated charcoal is filled only in various types of different towers in different ways.
Recently, planned sites for new semiconductor and liquid crystal factories tend to be vast places or areas of inexpensive land prices. Such areas are in many cases those remote from cities and good in natural environments (areas good in water quality of rivers and free from air pollution), generally.
In particular, in areas with good natural environments, the river into which factory waste water is discharged may be so good in water quality as can be classified as a clear stream. Such rivers with good water quality mean water areas of lean saprobic or .beta.-median saprobic water areas in terms of the soil water biology system. The .beta.-median saprobic water areas refer to slightly dirtied water areas where ayu fish or fireflies are living.
In such an area with a good natural environment, for an apparatus for waste water treatment or an apparatus for prevention of air pollution to be planned with emphasis laid on the environment of the area, there is a possibility that the environment of the area may be adversely affected by the plan even if the legal regulation levels and municipal regulation levels are merely observed. Accordingly, it is necessary to reduce the load given to environments by effluent water and discharged exhaust gases as much as possible. More specifically, it is insufficient for the effluent waste water to be only legally acceptable in measurement of water quality. The effluent water will not become treated water having a good impression for the local residents unless it is treated to such a level as will neither be foamed by a slight amount of hard-to-decompose surfactant nor generate any slight malodorous gas. Further, from the background for the water quality of effluent water discharged by semiconductor factories and liquid crystal factories, there are increasing numbers of cases where local residents will not easily accept new plans of waste water treatment. In the current days, in which such a regional environment has been reached that local residents demand strict level of treated water, it is necessary to take into account not only ecosystems surrounding the whole area but also appearances of treated water. Consequently, the present situation is that there is a desire for development of an apparatus and method for waste water treatment which will not change the local environment, nor give any influence on the local environment, and which is high in level and properly economical, and moreover which is well designed in terms of cubic structure so as to involve a less installation area.
In contrast to this, the above-mentioned conventional counterpart is purposed to achieve waste water treatment so that only legal restrictions are observed in respects of TMAH, surfactants, alcohols, and resists. As a result, even after the waste water treatment is executed, slight amounts of hard-to-decompose surfactants and slight amounts of resists may remain in the treated water. The hard-to-decompose surfactants may be a cause for a slight amount of foam in the treated water. Also, the light amounts of resist will color the treated water yellowish. The conventional counterpart has not been cared for economically preventing these slight amounts of foaming and coloring in the treated water.
In the semiconductor factories and liquid crystal factories, even foaming due to surfactants derived from treated water and coloring of resist components of treated water would matter for the neighbor residents from the viewpoint of maintaining the local environment. In particular, when the water of the effluent river is utilized as agricultural water, it would matter for the neighboring residents.
As the measures for this problem, i.e., measures for slight amounts of surfactants and coloring components in the treated water at the final stage of waste water treatment, the aforementioned activated charcoal adsorption treatment is commonly adopted. However, the activated charcoal adsorption treatment has a drawback that the activated charcoal will decrease in amount of adsorption in a certain period so that its service life is short, arising a need of carrying the activated charcoal to the outside and regenerating it.
Recently, there have been developed various types of treatment apparatus using activated charcoal with microorganisms (Japanese Patent Laid-Open Publications HEI 2-229595 and HEI 4-260497). Those are however designed for no more than water purification of relatively good water quality and, in particular, not designed for treatment of waste water containing hard-to-decompose surfactants that would take considerable time. Besides, the apparatus are those which use granular activated charcoal with high initial cost. Also, those apparatus use various types of methods or systems to fill activated charcoal in the particular tower for use of activated charcoal charge, thereby achieving water purification.
Further, the activated charcoal utilized in the above apparatus for high-level waste water treatment are in most cases granular activated charcoal involving relatively high initial cost, whether coconut shell based or coal based. This causes the apparatus for waste water treatment to increase in its initial cost, with the result of worse economy.
Also, in most cases, the time of contact with activated charcoal in the activated charcoal tower is within 2 hours. Therefore, the time for which microorganisms act especially on hard-to-decompose chemical substances is insufficient for reliable treatment to be expected. Although it is possible to design for a sufficient time of contact with activated charcoal if necessary, the conventional method of activated charcoal treatment would result, impracticably, in high initial costs of treatment facilities because of a large quantity of activated charcoal with high unit prices in order to ensure contact reaction time of 6 hours or more for influent water. In either case, the activated charcoal would result in high initial costs for facilities, impracticably.
Meanwhile, malodorous gas is generated from the aforementioned factories, although in very small amounts. More specifically, they include malodorous gases derived from chemicals used in production processes and special gases, malodorous gases generated from source tanks and the like for household waste water treatment and production system waste water treatment, and the like. Even these malodorous gases of small amounts may matter in districts with particularly good environments. However, although such malodorous gases of small amounts would matter, planning general apparatus for malodorous gas treatment would cause increase in construction cost and maintenance cost, problematically. In other words, there is a desire for means for malodorous gas treatment that requires extremely low initial cost and running cost. Several treatment systems have conventionally been available as the means for treatment of malodorous gases, including the scrubber system with washing by chemicals or water, the adsorption system with the use of activated charcoal and the combustion system. However, as a matter of course, they have encountered great problems of initial cost, running cost, maintenance, large installation spaces, and the like.
In particular, as in the aforementioned semiconductor factories and liquid crystal factories, apparatus for malodorous gas treatment should be planned when, even if legally acceptable, malodorous gases may be generated more or less so as to give rise to neighboring residents' claims. However, actually, it is excessive and uneconomical to provide a full-scale apparatus for malodorous gas treatment in order to solve such a small amount of malodor.
When granular activated charcoal is adopted as in the conventional system, there would be a problem that the granular activated charcoal may flow out of the apparatus if the back washing flow rate fails to be properly controlled in the process of back washing, because the activated charcoal is granular.
In either case, the conventional apparatus and method would tend to result in insufficient treatment in the case where high concentration toxic waste water containing large amounts of hard-to-decompose surfactants and resist components, which both would be hard to biodecompose and demanding considerable time for treatment, is to be treated in conformity to local environments. Thus, there is a possibility that, needless to say, the treated water may foam, but also that the water quality of effluent districts may undergo change that would affect the ecosystem of the effluent districts.
The reasons of the above include: (1) since the surfactants and resist components used in the aforementioned factories are hard-to-decompose chemical substances that have difficulty in biodecomposition, the conventional various types of methods using activated charcoal would be such that the activated charcoal, even if first act for adsorption to some extent, would soon come to an end of life such as not to act for adsorption; and (2) even with the use of activated charcoal with microorganisms, since the surfactants are hard-to-decompose, a contact reaction time of only 2 hours or so is insufficient, such that the hard-to-decompose chemical substances could not be biodecomposed with reliability and efficiency.
As shown above, the conventional method of waste water treatment has a problem that, with respect to the high concentration waste water of the aforementioned factories, surfactants, which are small amounts of hard-to-decompose chemical substances that would take considerable treatment time, and small amounts of organic substances and coloring components could not be treated economically and reliably even if activated charcoal is used.
The following description is based on experimental results. Even if the high concentration toxic waste water treated without dilution by the conventional method of waste water treatment is considered to be sufficiently safe on the basis of its analytical values from the standard of the current analytical technique, there will arise a phenomenon that foaming is caused by the small amounts of surfactants provided that effluence gap exists in the flow of effluence. This foaming phenomenon, although legally acceptable, may be misunderstood to be imperfect as treatment from the standpoint of neighboring residents. Further, when the high concentration waste water is treated by increasing the concentration of microorganisms without dilution, both the microorganism concentration and the waste water concentration are high in the aeration tank so that slight amounts of organic malodorous gases will be generated. Meanwhile, the treated water having such quality that larger quantities of foams due to hard-to-decompose surfactants are generated could not be said to be safe to small fish living in the rivers of the aforementioned good natural environment districts and to the biological ecosystem of marsh snails, which are a kind of snail that is a feed for fireflies. Those local creatures such as small fish and marsh snails generally have low resistance to environmental changes so that they could not live in the treated water, especially when the treated water is derived from treatment of the high concentration waste water only by the conventional method without dilution.
The concrete reason that the above local creatures of the above district could not live in the above treated water can be considered that since the high concentration waste water is treated without dilution, a large amount of decomposed organic substances remain, and that the conditions of small amounts of hard-to-decompose surfactants and organic substances are insufficient for the creatures to live in the treated water.
As for the appearance of the treated water, since the high concentration waste water of the above factories is colored in the waste water itself, the conventional treatment method without dilution would involve the colored treated water. Therefore, if the treated water is discharged into rivers that can be said to be clear streams, there may arise a problem.
Meanwhile, a method of treatment not without dilution but by diluting the high concentration waste water to ten times or so is also available. However, in this case, the waste water treatment facilities involved would be very large scale, uneconomically.
To summarize up the above description, the conventional method for waste water treatment with an activated charcoal tower is disadvantageous in the following points:
(1) Even if the treated water discharged into public water regions with good environments satisfies the above-mentioned legal restriction values and regulation values, a gap between effluent piping and effluent public water region, if any, would cause the foaming phenomenon due to small amounts of hard-to-decompose surfactants, resulting in bad appearance. Also, the colored substances, if not completely treated, would also cause bad appearance. A matter of course as it is, the conventional activated charcoal tower could not treat malodorous gases. In addition, in principle, the activated charcoal tower could not treat nitride, phosphorus, and salts. PA1 (2) The waste water treated by the conventional method has such water quality as may affect aquatic animals vulnerable to environmental pollution, such as small fish and marsh snails. Therefore, the conventional method may adversely affect the earth environment. PA1 introducing treatment-object water pretreated in a pretreatment process into a contact circulation part having a cultivation bed on which an aquatic plant has been grown and charcoal in which microorganisms have been grown, so that the contact circulation part is submerged in the treatment-object water; PA1 introducing malodorous gas to the contact circulation part; PA1 lifting the treatment-object water from the contact circulation part by an air lift pump and sprinkling the treatment-object water onto a sprinkling circulation part having the charcoal in which microorganisms have been grown; and PA1 returning the treatment-object water that has passed through the sprinkling circulation part to the contact circulation part.
In other words, in effluent regions which are free from environmental disruption and have a small amount of river water, like the recent planned sites for semiconductor factories and liquid crystal factories, the treated water, even if it meets regulation values such as described above so as to be legally acceptable, may often affect the biological ecosystem. As a result, if such treated water is discharged, there arises a great danger of destroying the biological ecosystem of creatures vulnerable to environmental disruption, which is a problem.
For example, from experimental results, it is shown that even if the high concentration toxic waste water is treated without dilution and passed through the activated charcoal tower so that the waste water satisfies the legal restrictive values, aquatic animals vulnerable to environmental disruption, such as small fish and marsh snails, could not live in the treated water.
Furthermore, there has so far been unavailable any apparatus for waste water treatment, which can treat not only waste water containing hard-to-decompose surfactants and resist components but also malodorous gases at the same time and which can reduce the initial cost and the running cost.